It was not enough, however, simply to find some metal and get a blacksmith to bash it into shape.

Pratchett, believing the sword would not truly be his own unless it was made from metal he had produced, found a field with deposits of iron ore near his home in Wiltshire, west of London.

He gathered the deposits and smelted the iron ore himself.

The author, 62, who has sold about 65 million copies of his books, which include the Discworld series, said: "Most of my life I've been producing stuff which is intangible and so it's amazing the achievement you feel when you have made something which is really real."

With help from his friend Jake Keen — an expert on ancient metal-making techniques — the author dug up 81kg of ore and smelted it in the grounds of his house, using a makeshift kiln built from clay and hay and fuelled with damp sheep manure.

Pratchett, who has Alzheimer's disease, also said he had throw

n in "several pieces of meteorites — thunderbolt iron, you see — highly magical,

you’ve got to chuck that stuff in whether you believe in it or not".

After days of hammering the metal into bars, he took it to a blacksmith, whom he helped to shape it into a blade, which was finished with silverwork.

Pratchett has stored the sword, which he completed last year, in a secret location, apparently concerned about the authorities taking an interest in it.

He said: "It annoys me that knights aren’t allowed to carry their swords. That would be knife crime."